Chlorinated polymers are useful as a burning-resistant material, and chlorinated polymers having a narrow molecular weight distribution are useful as a radiation-sensitive resist material.
It is known to improve certain properties of polymers by chlorinating the same. For example, a process for chlorinating polystyrene in a solvent such as carbon tetrachloride and in the presence of a catalyst, such as, for example, a peroxide such as benzoyl peroxide or the like, by using a chlorinating agent such as chlorine, N-chlorosuccinimide, sulfuryl chloride, etc., is described, for example, in Japanese Patent Application (OPI) No. 16995/1973, U.S. Pat. No. 3,812,061, etc. (The term "OPI" as used herein refers to a "published unexamined Japanese patent application".)
Chlorinated polyvinyltoluene having a narrow molecular weight distribution, which is useful as a radiation-sensitive resist material having high resolution and superior dry-etching resistance, is described, for example, in Japanese Patent Application (OPI) No. 187923/1983, etc.
These methods, however, have disadvantages such as depolymerization is induced in chlorination, the molecular weight of the polymer is remarkably lowered, and the mechanical properties of the polymer are deteriorated. For example, see Journal of Applied Polymer Science, Volume 12, Page 2065 (1968).
A technique where a polymer, as a raw material, can be chlorinated so as to be provided with burning resistance, fusion resistance, thermal resistance, etc., without damaging its desirable properties, has been desired for a long time.
A process has been proposed for preparing chlorinated polymers with only a slight disturbance in the molecular weight distribution of the polymers, is described in Japanese Patent Application (OPI) No. 42779/1983 (corresponding to U.S. Pat. No. 4,414,065). According to the method described in U.S. Pat. No. 4,414,065, it is, however, necessary to isolate the polymers and, hence, it is impossible to prepare highly chlorinated polymers, i.e., polymers which contain more than 0.5 mol of chlorine per unit monomer, without disturbing the molecular weight distribution of the mother polymer.